This invention relates generally to acetals and more particularly to acetals containing nitro groups.
Formals and acetals of polynitro - and halonitroethanols (e.g., 2,2,2-trinitroethanol, 2,2,2-fluorodinitroethanol, 2,2-dinitropropanol, 2,2,2-difluoronitroethanol) are of considerable interest as explosive and propellant ingredients. For example, acetals and formals of 2,2-dinitropropanol and 2,2,2-fluorodinitroethanol have been used extensively as energetic plasticizers in various composite propellants and explosives. Special synthesis methods had to be discovered for the preparation of these materials since the extremely low reactivity of the parent alcohols rendered useless the conventional methods for acetal and formal preparation. Thus, U.S. Pat. No. 3,526,667 describes a method for the preparation of formals of nitroalcohols consisting of the condensation with formaldehyde in concentrated sulfuric acid as reaction medium. A method for the preparation of fluorodinitroalkyl acetals, U.S. Pat. No. 3,629,338, uses BF.sub.3 and similar acidic catalysts to effect condensation of acetaldehyde with fluorodinitroalkanols.
However, efforts to employ these methods to prepare acetals and formals derived from aldehydes other than formaldehyde and acetaldehyde have been largely unsuccessful. Especially aldehydes with negative (i.e., electron-withdrawing) substituents were found to be unreactive under the conditions used by these methods. For example, concentrated sulfuric acid fails to catalyze acetal formation between CCl.sub.3 CHO, CF.sub.3 CHO, and HOOCCHO aldehydes and (NO.sub.2).sub.2 FCCH.sub.2 OH.